fix: restore audio refactor + features lost in #419 squash-merge (#429)

The squash-merge of PR #419 was performed against an outdated PR base
that predated several main-side refactors and features. The resulting
squash inadvertently re-introduced files that had already been removed
(`src-tauri/src/audio.rs` monolith, `app-icon.png`) and reverted main's
content for ~20 files (`src-tauri/src/lib.rs` decompose, `src/App.tsx`
animation-pause, `src/components/AlbumRow.tsx` headerExtra, etc).

This commit:

* Restores all collateral-damage files to their pre-#419 main state
  (5662dafe), including the audio module split, lib decompose,
  Cargo.toml `windows` dep, animation-pause-on-blur logic, and
  `reducedAnimations` toggle plumbing in WaveformSeek/Settings.
* Keeps the genuine #419 work intact: tri-state duration toggle,
  position counter, persistent Now Playing collapse, animated EQ
  indicator (in QueuePanel.tsx, 8 locales, authStore, components.css).
* Merges authStore.ts so both `reducedAnimations` (from #426) and
  `queueNowPlayingCollapsed` (from #419) coexist.
* Adds the `.eq-bars.paused` CSS rule manually since components.css
  needed a 5662dafe base + the single #419 addition.
* Fixes a latent type error in OverlayScrollArea.tsx (`useRef<T>(null)`
  is `RefObject<T>` / read-only under current `@types/react`; widened to
  `useRef<T | null>(null)` so the existing `wrapRef.current = el`
  assignment compiles).

Verified locally with `cargo check` and `npm run build` — both green.

src/components/AlbumTrackList.tsx

@@ -119,6 +119,7 @@ const TrackRow = React.memo(function TrackRow({
   const isActive = currentTrackId === song.id;
   // Primitive selector: row only re-renders when *this song's* preview state flips.
   const isPreviewing = usePreviewStore(s => s.previewingId === song.id);
+  const isPreviewAudioStarted = usePreviewStore(s => s.previewingId === song.id && s.audioStarted);
 
   const renderCell = (colDef: ColDef) => {
     const key = colDef.key as ColKey;
@@ -156,7 +157,7 @@ const TrackRow = React.memo(function TrackRow({
             </button>
             <button
               type="button"
-              className={`playlist-suggestion-preview-btn${isPreviewing ? ' is-previewing' : ''}`}
+              className={`playlist-suggestion-preview-btn${isPreviewing ? ' is-previewing' : ''}${isPreviewAudioStarted ? ' audio-started' : ''}`}
               onClick={e => {
                 e.stopPropagation();
                 usePreviewStore.getState().startPreview({ id: song.id, title: song.title, artist: song.artist, coverArt: song.coverArt, duration: song.duration }, 'albums');